The present invention relates to an LC oscillator that can be formed on various kinds of substrates such as a semiconductor substrate.
There is known such a semiconductor circuit that forms a spiral pattern electrode on a semiconductor substrate by using thin film forming technique, and uses this pattern electrode as an inductor element. When current flows in such an inductor element that is formed on a semiconductor substrate, magnetic flux is generated in the direction perpendicular to a spiral pattern electrode. Nevertheless, since eddy currents are induced on the front side of the semiconductor substrate by this magnetic flux to cancel effective magnetic flux, there is such a problem that doesn""t effectively function as the inductor element. In particular, since the higher a frequency of a signal which flows in the inductor element becomes, the more remarkable this inclination becomes, and consequently it is difficult to form an LC oscillator, including the inductor element as a resonance element, on a semiconductor substrate.
The present invention is achieved in view of such a point. Its object is to provide an LC oscillator that can perform oscillation even if the LC oscillator is formed on a substrate.
An inductor element included in an LC oscillator of the present invention has two conductors that are formed in piles on a substrate in the state where they are mutually insulated, and are connected with each other at both odd ends. While one conductor separating from the substrate is used as an inductor conductor, a lead wire of this inductor conductor is led out through a gap between another conductor, being near the substrate, and the substrate. It is experimentally confirmed that an inductor element that has such structure has predetermined inductance without losing an inductance component by eddy currents etc. even if the inductor element is formed on a substrate. With using this inductor element as a part of an LC oscillator, oscillation can be performed even if the LC oscillator is formed on the substrate. In particular, by leading out the lead wire of this inductor conductor included in the inductor element from between another conductor and the substrate, it becomes possible to preventing the flow of the effective magnetic flux, generated by the inductor conductor, to the minimum from being interrupted. Hence good characteristics can be obtained.
In case where the inductor element described above has three or more layers of metal layers formed on the substrate, it is desirable to form the two conductors described above and lead wires respectively with using different metal layers which are mutually apart by one or more layers. Since the inductor conductor can be made to be apart from the lead wires by at least two or more layers by adopting such constitution of the inductor element included in the LC oscillator, it is possible to further reduce the influence of the electric current that flows in the lead wires.
In addition, it is desirable to connect the two conductors included in the inductor element mentioned above at both odd ends with using a part of a lead wire of the inductor conductor extending from the one end of the inductor conductor. Since the number of the conducting wires (lead wires and connecting wires) that intersect the inductor conductor can be reduced, a degree of interrupting the flow of the effective magnetic flux generated by the inductor conductor can be further reduced. In addition, since the shape of a mask can be simplified when manufacturing each conductor and lead wires with using an aligner etc., it is possible to reduce a cost and labor hours for manufacturing the whole of the LC oscillator.
Furthermore, an inductor element included in the LC oscillator of the present invention has two conductors that are formed in piles on a substrate in the state where they are mutually insulated, and are connected with each other at both odd ends. While using one conductor apart from the substrate as an inductor conductor, one end of another conductor not connected to the inductor conductor is terminated with a predetermined impedance element. Although electric current flows also in another conductor by the effective magnetic flux generated by the inductor conductor in the inductor element, it becomes possible to prevent unnecessary reflection in this portion and to improve characteristics of the inductor element by terminating the end of the free side of another conductor with the impedance element. Hence, oscillation can be performed reliably by the LC oscillator comprising the inductor element. In addition, it is possible to adjust frequency characteristics or the like of another conductor by forming the impedance element described above with using any of a resistor, a capacitor, and an inductor or combining these. Hence it becomes possible also to adjust oscillation characteristics finely by adjusting a device constant of the impedance element at a suitable value.
In addition, it is desirable to adjust termination conditions by making it possible to change at least one device constant of a resistor, a capacitor, and an inductor, which constitute the impedance element described above, and making this device constant variable. By some external means, for example, by changing a value of a control voltage applied, it becomes possible to adjust a device constant of the whole impedance element, that is, characteristics of the inductor element by a change of termination conditions. It also becomes possible to adjust finely an oscillation frequency.
In particular, when the substrate described above is a semiconductor substrate, it is desirable to form the capacitor where a device constant can be changed by a variable capacitance diode. While it becomes possible to miniaturize parts by using the variable capacitance diode formed with using the semiconductor substrate, it becomes possible to reduce a cost for manufacturing LC oscillator by simplifying manufacturing process in comparison with the case where external parts are attached thereafter, and wiring etc. are performed. Similarly, when the substrate described above is a semiconductor substrate, it is desirable to form a variable resister made of an FET whose channel is used as a resistor. While it is possible to miniaturize parts by using the variable resistor made of the FET formed with using the semiconductor substrate, it becomes possible to reduce a cost for manufacturing LC oscillator by simplifying manufacturing process in comparison with the case where external parts are attached thereafter, and wiring etc. are performed.
In addition, it is desirable to form an inductor, which constitutes the impedance element, by a conductive layer formed on the substrate in predetermined shape. Since high Q is not required of the inductor used for terminating one end of a conductor, it is possible to realize the inductor with a conductor pattern on the substrate. Moreover, since it becomes possible to form this conductor pattern at the same process with using a metal layer for performing various kinds of wiring etc., it becomes possible to perform miniaturization of entire LC oscillator, simplification of process, and cost reduction.
In addition, as a substrate mentioned above, it is preferable to use a semiconductor substrate, and to form each configuration parts of LC oscillator on the substrate. If the inductor element that effectively functions can be formed on a semiconductor substrate, it is possible to form each configuration parts for LC oscillator, including the inductor element, on the semiconductor substrate. Hence it becomes possible to form the whole of the LC oscillator on the semiconductor substrate without using any external parts.
In addition, it is desirable to form two conductors, described above, in the substantially same shape or long shape. Since an upper conductor never directly faces the front side of the substrate owing to making the two conductors the same in shapes, it is possible to reduce the eddy currents that are generated on the substrate when the upper conductor directly faces the substrate. In addition, it is possible to give predetermined inductance to the upper conductor by making the shapes of the two conductors be long. In particular, since it is possible to give large inductance to a conductor when the conductor is formed in one or more turns of spiral shape or a meander shape, the conductor is suitable for being built in an LC oscillator having comparatively low frequency. In addition, since it is possible to give a small inductance to a conductor when the conductor is formed in a circular shape less than one turn or an substantially linear shape in comparison with the case where the conductor is formed in a spiral shape or the like, the conductor is suitable for being built in an LC oscillator having comparatively high frequency.
Moreover, when two conductors are made in spiral shapes, it is preferable to connect an inner end of one conductor with an outer end of another conductor. Since it is experimentally confirmed that it is possible to secure further large inductance when an inductor conductor is formed on a substrate owing to performing such connection, it is possible to realize the inductor element that effectively functions on a substrate. In particular, when the shape is a spiral one having one or more turns, it is necessary to extend a lead wire from the inner circumferential end of the inductor conductor having this spiral shape. Nevertheless, it is possible to suppress to the minimum the interruption of flow of the effective magnetic flux, generated by the inductor conductor, by leading out the lead wire between the conductor, being near the substrate, and the substrate.
In addition, the inductor element described above is suitable for use as a compound element that also has a capacitance component besides an inductance component. Since this inductor element has two conductors, mutually superimposed, and a capacitance component is also included in its characteristics, the characteristics of this inductor element can be effectively used by using this inductor element as one part of the LC oscillator where an inductor and a capacitor are used in combination.